Transmission electron micrographs of Opossum spermatogonia showing different regions within the nucleolus. One region is more lightly staining and fine textured, the other denser and more coarsely tex...

Transmission electron micrograph showing the highly compact nucleolus in the salamander hepatocyte. A finer textured central region is surrounded by a coarser region.

Transmission electron micrograph of Leydig cell nucleus from the domestic boar contains a region (arrow) thought to represent the single X chromosome which is largely heterochromatic. The chromosome i...

Transmission electron micrographs showing details of nuclear pores in thin sections of an erythroblast (above) and endothelial cell (below). Pores appear to be filled with dark staining material in th...

Electron micrograph of a thin section of fixed, embedded stained cells of Peranema trichophorum. Shown is a section of the "rodorgan', a bundle of 13-protofilment microtubules with pseudo-hexagonal sy...

Drosophila melanogaster thoracic tergotrochanter muscle from a four week-old wild-type animal. A longitudinal section of myocyte is displayed. Sections of parallel myofibrils are seen with distinguish...

At cyst formation in the 'giant' unicellular green alga Acetabularia, each cyst contains a single nucleus which subsequently undergoes several rounds of mitosis prior to gamete formation. Initially t...

Transmission electron micrograph illustrating the 'classic' appearance of the nucleus in osmium tetroxide fixed material. In this pancreatic acinar cell nucleus, the only prominent feature is the lar...

Transmission electron micrograph of a bone marrow orthochromatic erythroblast from guinea pig showing terminal differentiation in erythrocyte formation. Accompanying the cessation of most transcriptio...

Transmission electron micrograph of a cross section through the nucleolus from a Chinese hamster spermatogonium revealing a complex distribution of regions of varying granular textures.